Turbocharger

ABSTRACT

A sealing structure includes a labyrinth seal provided between a housing and an outer periphery of an end portion of a turbine shaft on a turbine wheel side, and a piston ring seal disposed on a side toward a center of the turbine shaft in an axial direction thereof from a position on the turbine shaft at which the labyrinth seal is provided, and a ring groove is formed along a circumferential direction of the housing in a middle portion of the labyrinth seal to reverse a flow direction of exhaust gas entering from the exhaust passage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a turbocharger which is employed inautomobiles or the like.

2. Related Art

Turbochargers which enhance output of internal combustion engines byblowing compressed air with increased density into inside of theinternal combustion engines are known as, for example, supercharger,turbocharger or the like.

A turbocharger, for example, is configured such that a turbine wheel isdisposed in an exhaust passage while a compressor wheel is disposed inan admission passage in an internal combustion engine such as anautomobile engine. These wheels are provided respectively on oppositeend portions of a turbine shaft that is housed within a shaft hole of ahousing. Within the shaft hole of the housing, rolling bearings supportrotatably the turbine shaft. When the turbine wheel is rotated byexhaust gas flowing through the exhaust passage, the turbine shaft andthe compressor wheel are rotated so that air inside the admissionpassage to be fed to the internal combustion engine is compressed.

Further, in the turbocharger as described above, a sealing structurethat performs sealing between the shaft hole and the exhaust passage aswell as between the shaft hole and the admission passage is providedsuch that lubricant which is provided with the shaft hole of the housingfor lubrication of the rolling bearing is not leaked out toward theexhaust passage and the admission passage and such that gas such as airor exhaust gas does not flow in the housing from the exhaust passage andthe admission passage. For example, piston ring seals are provided onouter peripheries of opposite ends of the turbine shaft in its axialdirection to form the sealing structure performing sealing between theshaft hole and the exhaust passage as well as between the shaft hole andthe admission passage (See, for example, JP-A-H11-101128 Publication).

In the conventional turbocharger, it is difficult to completely shut outleakage of the lubricant from the shaft hole of the housing to theexhaust passage and flow-in of the gas from the admission passage or theexhaust passage to the shaft hole. However, as reduction of lubricantcontamination in the exhaust gas is required in view of environmentalconsciousness, it is important to shut out fluid communication betweenthe exhaust passage and the shaft hole of the housing as much aspossible.

SUMMARY OF THE INVENTION

Accordingly, the object of the invention is to provide a turbocharger inwhich the fluid communication between the exhaust passage and the shafthole of the housing is effectively suppressed.

A turbocharger according to the invention includes:

a turbine shaft;

a turbine wheel disposed on a first end portion of the turbine shaft inan exhaust passage of an internal combustion engine;

a compressor wheel disposed on a second end portion of the turbine shaftin an admission passage of the internal combustion engine;

a rolling bearing rotatably supporting the turbine shaft within a shafthole of a housing; and

a sealing structure performing a sealing between the shaft hole and theexhaust passage,

wherein the sealing structure includes a labyrinth seal provided betweenan outer periphery of the first end portion of the turbine shaft and thehousing, and a piston ring seal disposed on a side toward a center ofthe turbine shaft in an axial direction thereof from a position on theturbine shaft at which the labyrinth seal is provided, and

wherein a ring groove is formed along a circumferential direction of thehousing in a middle portion of the labyrinth seal to reverse a flowdirection of exhaust gas entering from the exhaust passage.

According to the above construction, since the labyrinth seal providedbetween the outer periphery of the end portion of the turbine shaft onthe turbine wheel side and the housing is disposed as noncontactstructure without being brought into contact with the turbine shaft andthe shaft hole of the housing, it is possible to suppress that exhaustgas flows in from the exhaust passage without interfering with rotationof the rolling bearing. Further, it is possible to prevent the leakageof the lubricant to the exhaust passage by the piston ring seal that isdisposed on the side toward the center of the turbine shaft in the axialdirection thereof from the position on the turbine shaft at which thelabyrinth seal is provided. Moreover, by providing such inner/outerdouble sealing structure, the fluid communication between the exhaustpassage and the shaft hole of the housing is further suppressed.

In addition, by forming the ring groove along the circumferentialdirection of the housing in the middle portion of the labyrinth seal toreverse the flow direction of the exhaust gas entering from the exhaustpassage, it is possible to prevent effectively the inflow of the exhaustgas from the exhaust passage.

Further, by providing a coolant water jacket in which coolant water forcooling the turbine shaft is circulated is provided on a radial outerside of the turbine shaft from the position of the housing at which thelabyrinth seal is provided, the exhaust passage of the housing can becooled efficiently without extending a dimension of the turbine shaft inthe axial direction thereof. As a result, it is possible to suppressthat heat of the exhaust gas passing the exhaust passage is transmittedto the axial hole of the housing.

According to the invention, it is possible to suppress effectively thefluid communication between the exhaust passage and the shaft hole ofthe housing in the turbocharger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a turbocharger according to an embodimentof the invention.

FIG. 2 is an enlarged view of an essential portion of FIG. 1.

FIG. 3 is an enlarged view of a labyrinth seal portion of a turbochargeraccording to another embodiment of the invention.

FIG. 4 is an enlarged view of a labyrinth seal portion of a turbochargeraccording to another embodiment of the invention.

FIG. 5 is an enlarged view of a labyrinth seal portion of a turbochargeraccording to another embodiment of the invention.

FIG. 6 is an enlarged view of a labyrinth seal portion of a turbochargeraccording to another embodiment of the invention.

FIG. 7 is an enlarged view of a labyrinth seal portion of a turbochargeraccording to another embodiment of the invention.

FIG. 8 is an enlarged view of a labyrinth seal portion of a turbochargeraccording to another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the drawings.

FIG. 1 is a sectional view of a turbocharger according to an embodimentof the turbocharger. FIG. 2 is an enlarged view of an essential portionof FIG. 1. The turbocharger of the embodiment is a turbocharger for anautomobile engine, and includes a housing 40, and a turbine shaft 41housed in the housing 40 so as to be supported coaxially with an axis Cby being inserted into a pair of rolling bearings 10 a,10 b disposedapart from each other along the direction of axis C within the housing40. Further, in an exhaust passage 60, a turbine wheel 42 is provided onone end portion of the turbine shaft 41 and in an admission passage 61,a compressor wheel 62 is provided on the other end portion of theturbine shaft 41.

The housing 40 includes a housing body 40 a. The housing body 40 a has ashaft hole 43 at a center portion thereof that is formed in asubstantially cylindrical hole coincided with the axis C. In the shafthole 43, a tubular bearing holding member 15 is fitted into an innerperiphery 40 d of the housing body 40 a with a gap. The pair of therolling bearings 10 a, 10 b are fitted into the bearing holding member15 so as to support the turbine shaft 41 housed in the shaft hole 43rotatably around the axis C.

The pair of the rolling bearings 10 a,10 b (hereinafter called “rollingbearing(s) 10”) are provided with the same structure and disposedsymmetrically in the shaft hole 43 along the left and right direction inFIG. 1. A preload in the axial direction is applied to the rollingbearings 10 a, 10 b by urging the rolling bearings 10 a, 10 b outwardlyin the axial direction with an urging member 81 disposed between therolling bearing 10 a,10 b.

The rolling bearing 10 includes an inner ring 1, an outer ring 3 and anintermediate ring 2 disposed between the inner ring 1 and the outer ring3. A first rolling element set 4 and a second rolling element set 5 arearranged between the intermediate ring 2 and the inner ring 1, andbetween the intermediate ring 2 and the outer ring 3, respectively. Thefirst and second rolling element sets 4,5 are provided with balls 4 a,5a.

As shown in FIG. 1, in the rolling bearing 10, an inner peripheralsurface of the inner ring 1 serves as a fitting surface to the turbineshaft 41 such that the inner ring 1 is fitted around the turbine shaft41. A first bearing raceway 11 with which the balls 4 a of the firstrolling element set 4 are brought into contact is formed on an outerperipheral surface of the inner ring 1. An outer peripheral surface ofthe outer ring 3 of the rolling bearing 10 is fixed to an innerperiphery of the bearing holding member 15. A second bearing raceway 31with which the balls 5 a of the second rolling element set 5 are broughtinto contact is formed on an inner peripheral surface of the outer ring3. The intermediate ring 2 has a bent shape in its cross sectionextended along the axial direction of the bearing 10. A third bearingraceway 21 with which the balls 4 a of the first rolling element set 4are brought into contact is formed on a part of an inner peripheralsurface of the intermediate ring 2. A fourth bearing raceway 22 withwhich the balls 5 a of the second rolling element set 5 are brought intocontact is formed on a part of an outer peripheral surface of theintermediate ring 2.

The plural balls 4 a of the first rolling element set 4 are held by acage 8 along a circumference of a circle that is centered at the axis C.The plural balls 5 a of the second rolling element set are held by acage 9 along a circumference of another circle that is centered at theaxis C. The balls 4 a of the first rolling element set 4 and the balls 5a of the second rolling element set 5 have the same ball diameter oneanother. The balls 4 a of the first rolling element set 4 are broughtinto contact with the first bearing raceway 11 and the third bearingraceway 21 forming an opposite pair diagonally (namely, angularcontact). The balls 5 a of the second rolling element set 5 are broughtinto contact with the fourth bearing raceway 22 and the second bearingraceway 31 forming another opposite pair diagonally. The contact anglein both angular contacts is set to be the same, for example, to be 15°in FIG. 1. Accordingly, the rolling bearing 10 is capable of bearingload in the direction of the axis C (axial direction load). Further,since the rolling bearing 10 is arranged along the axial directionextending in the direction of the axis C, it provides a structure havinga damper function in the axial direction.

Damper members 7 are provided on outer peripheral surfaces of thebearing holding member 15 at its opposite ends in the direction of theaxis C to lessen vibrations generated due to rotation of the turbineshaft 41. The damper member 7 is fabricated by braiding metal wires toform a ring shape with a rectangular cross section. An outer peripheralsurface of the damper member 7 is brought into contact with the innerperiphery 40 d of the housing body 40 a. There are formed gaps (orvoids) partially or entirely between adjacent metal wires that form thedamper member 7. The damper member 7 is configured as a whole to beelastically deformable (contractible) in the radial direction and thedirection of the axis C by allowing elastic deformation of the metalwires within the gaps, or displacement among adjacent wires inlongitudinal directions of the wires in the damper member. The dampermember 7 is formed to have an outer diameter that is slightly largerthan an inner diameter of the shaft hole 43 so as to be interposedbetween the bearing holding member 15 and the shaft hole 43 in acompressed manner with a predetermined fitting margin in the radialdirection.

The gaps formed between the metal wires in the damper member 7 arefilled with lubricant. Fluorinated grease is used for such lubricant forexample.

By providing the damper member 7, the vibration transmitted from theturbine shaft 41 to the bearing holding member 15 through the rollingbearings 10 is damped by the damper members 7 and transmitted to thehousing 40 in the turbocharger. At this time, the damper members 7 areelastically deformable in the radial direction and the direction of theaxis C. Therefore, the vibration can be damped three-dimensionally or inall directions and an excellent damping function is performed. Further,not only elastic deformation of the metal wires themselves but frictionscome from the braiding structure and entanglement of the metal wiresalso serve to store and dissipate the vibration energy in all directionsbeyond simple effect of viscoelasticity.

In addition, since the damper member 7 is formed with metal wires,excellent heat resistance can be also provided. Therefore, it issuitable for a damper means for a turbo charger used in very hightemperature.

Further, since grease is filled in the gaps of the wires in the dampermember 7, wires are hardly worn by being rubbed against each other.

Furthermore, by inserting the damper member 7 as described above betweenthe bearing holding member 15 and the housing 40, any oil film damperprovided conventionally is not needed. Accordingly, it is possible toaccomplish simplification of the structure of the housing 40 as well ascost reduction.

In the turbocharger as described above, a lace member 36 is providedsuch that one end thereof is put into a tank portion in which thelubricant is stored and the other end thereof is placed in the rollingbearing 10 within the shaft hole 43. Thus, lubrication of the rollingbearing 10 is conducted by feeding the lubricant from the tank portion(not-shown) to the shaft hole 43 utilizing capillary action of the lacemember 36. By means of the lace member 36, which does not require anypower, the lubricant is fed to the rolling bearing 10 in the shaft hole43 even in a condition that rotation of the turbine shaft 43 is stopped.For the lubricant stored in the tank portion, oil which is normally usedfor lubrication of the rolling bearing and which has a suitableviscosity to be able to percolate in the lace member 36 can be used inthe embodiment. Among such oils, oil which is superior to engine oils inseizure resistant property is preferably used, for example, chemicalsynthetic oil such as polyol ester oil, diester oil, aromatic ester oil,synthetic hydrocarbon oil, ether oil, silicon oil and fluorine oil.

Inside of the housing body 40 a of the housing 40, a coolant waterjacket 26 in which coolant water is circulated is provided. The coolantwater jacket 26 is formed so as to surround the turbine shaft 41 on aradial outer side of the rolling bearings 10 from one end portion 49 onthe exhaust passage 60 side to the other end portion 50 on the admissionpassage 61 side in the housing body 40 a. In other words, the coolantwater jacket 26 is formed so as to surround the shaft hole 43 along thecircumferential direction of the turbine shaft 41.

Further, in the coolant water jacket 26, an annular recess 33 indentinginwardly from the inner peripheral surface 43 a of the shaft hole 43 inthe radial direction of the turbine shaft 41 is formed on the one endportion 49 of the housing body 40 a. Thus, by interposing the annularrecess 33 between the turbine wheel 42 and the rolling bearing 10 a inthe axial direction, it is possible to conduct heat exchange effectivelybetween heat transmitted from the exhaust passage 60 and the coolantwater in the annular recess 33. Therefore, it is possible to reduce heattransmission from the turbine wheel 42 side to the shaft hole 43. As aresult, it is possible to suppress thermal degradation of the lubricantand the rolling bearing 10 provided within the shaft hole 43.

Furthermore, in the turbocharger according to the embodiment, a pistonring seal 44 a and a labyrinth seal 9 are provided between the rollingbearing 10 and the turbine wheel 42 so as to be adjacent to each otheralong the axis C in order to form a seal structure to suppress fluidcommunication between the shaft hole 43 and the exhaust passage 60.

As shown in FIG. 2, the piston ring seal 44 a is adjacent to the rollingbearing 10 a in the direction of the axis C. The piston ring seal 44 ais configured by disposing a piston ring 47 a between a ring groove 46formed on an outer peripheral surface of a sleeve 45 a that is fittedaround the turbine shaft 41 so as to rotate together with the turbineshaft 41 and a cylindrical portion 40 b of the housing 40 projectingtoward the shaft hole 43. A minute gap is formed between the ring groove46 and the piston ring 47 a so that a gap between the sleeve 45 a andthe cylindrical portion 40 b is closed. By such structure, it ispossible to suppress that the lubricant within the shaft hole 43 ismoved to the turbine wheel 42 side and also possible to suppress thatexhaust gas flows in to the shaft hole 43 from the exhaust passage 60.

As shown in FIG. 2, the labyrinth seal 9 is provided on the turbinewheel 42 side from the piston ring seal 44 a. The labyrinth seal 9 isprovided by fitting the turbine shaft 41 with a predetermined small gapto a cylindrical sleeve 90 that is provided at a center portion of asidewall 17 on the exhaust passage 60 side of the housing body 40 a.

In the sleeve 90 forming the labyrinth seal, on an intermediate portionthereof along the axis C, two ring grooves 91 provided adjacent to eachother are formed in an indented manner in the radial direction. Further,on the turbine shaft 41 side on which the labyrinth seal is formed, aring groove 41 a is formed in an indented manner in the radialdirection. On an inner peripheral surface of the sleeve 90, a projectionportion 92 is formed so as to have a top portion defined by a taperedsurface that is flared out from the turbine wheel 42 side to the shafthole 43 side. By this structure, the exhaust gas directing from theturbine wheel 42 side to the shaft hole 43 side does not movestraightforwardly to the shaft hole 43 side, and it is easily introducedto the ring groove 91. By means of the labyrinth seal 9, when theexhaust gas directing from the turbine wheel 42 side to the shaft hole43 side reaches at a space defined by the ring groove 91, the projectionportion 92 and the outer periphery of the turbine shaft 41, turbulenceis generated by pressure change (stepwise pressure decrease) so that theexhaust gas does not easily advance toward the shaft hole 43. Therefore,the sealing performance is improved as compared with the structure inwhich only a small gap is formed.

As described above, by providing the labyrinth seal 9, the inflow of theexhaust gas from the exhaust passage 60 side into the shaft hole 43 isfurther suppressed. In addition, the labyrinth seal 9 is noncontactstructure, no friction is generated. As a result, performance of thesealing structure is further increased without interfering with rotationof the turbine shaft 41.

In the above described embodiment, the rolling bearing 10 and thelubricant within the shaft hole 43 can be disposed away from the exhaustpassage 60 by the labyrinth seal 9, so that heat from the exhaustpassage side 60 is not easily transmitted to the rolling bearing 10 aand the lubricant within the shaft hole 43. Therefore, it is possible tosuppress thermal degradation of these parts. Further, the annular recess33 of the coolant water jacket 26 is formed by utilizing the additionalspace on the outer side in the radial direction that is created forproviding the labyrinth seal 9. Therefore, it is possible to suppressthat the size of the turbocharger is unduely increased.

As shown in FIG. 1, in the turbocharger according to the embodiment, asa sealing structure performing sealing between the shaft hole 43 of thehousing 40 and the admission passage 61, a piston ring seal 44 b havingsubstantially the same structure as the piston ring seal 44 a providedon the exhaust passage 60 side is provided. The piston ring seal 44 b isprovided adjacent to the rolling bearing 10 b in the direction of theaxis C. The piston ring seal 44 b is configured by disposing two pistonrings 47 b between two rows of ring grooves 48 formed on an outerperipheral surface of a sleeve 45 b that is fitted around the turbineshaft 41 so as to rotate together with the turbine shaft 41 and an innerperipheral surface of an opening portion 40 c formed at the center of asidewall 18 of the housing 40. A minute gap is formed between each ringgroove 48 and each piston ring 47 b so that the gap between the sleeve45 b and the inner peripheral surface of the opening portion 40 c isclosed. By such structure, it is possible to suppress that the lubricantin the shaft hole 43 moves into the compressor wheel 62 side and thatthe exhaust gas flows in to the shaft hole 43 from the admission passage61 side.

The invention is not limited to the embodiment as described above. Forexample, the shape of the labyrinth seal 9 is not limited as long as itdoes not go against the purpose of the invention. FIGS. 3-8 showturbochargers according to other embodiments of the invention.

A turbocharger according to an embodiment shown in FIG. 3 has alabyrinth seal 9 in which a ring groove 91 and a projection portion 92,forming a pair, are added in the labyrinth seal 9 shown in FIG. 1 andFIG. 2.

Turbochargers according to embodiments shown in FIG. 4 and FIG. 5 havelabyrinth seals 9 in which ring grooves 41 a and projection portions 41b with flat top faces are formed in the turbine shaft 41. In theturbocharger according to the embodiment shown in FIG. 4, a projectionportion 92 projecting toward the axis C of the housing 40 is formed onan inner peripheral surface of the sleeve 90 on the turbine wheel 42side. A gap formed between a top end portion of the projection portion92 and the outer peripheral surface of the turbine shaft 41 is set to bevery small. On the other hand, the turbocharger according to theembodiment shown in FIG. 5, a projection portion 92 is formed on aninner peripheral surface of the sleeve 90 on the shaft hole 43 side. Agap formed between the projection portion 92 and the outer peripheralsurface of the turbine shaft 41 is set to be very small.

Turbochargers according to other embodiments shown in FIGS. 6 and 7,each has a labyrinth seal 9 in which ring grooves 41 a are formed on theturbine shaft 41.

A turbocharger according to an embodiment shown in FIG. 8 has alabyrinth seal 9 in which projection portions 92 with flat top faces andring grooves 91 are formed. Side faces of the ring grooves 91 and theprojection portions 92 are tapered.

Further, in order to further suppress fluid communication between theshaft hole 43 of the housing 40 and the admission passage 61, alabyrinth seal 9 may be formed coaxially on a radial outer side of thepiston ring seal 44 b of the turbine shaft 41. In such a case, forexample, the labyrinth seal 9 is configured by forming a ring groove onthe housing 40 opposing to the outer periphery of the turbine shaft 41at its end on the compressor wheel 62 side, or on the outer periphery ofthe turbine shaft 41 at its end on the compressor wheel 62 side, so asto extend along the circumferential direction of the turbine shaft 41.

Further, lubrication methods of the rolling bearings 10 may be a fullfloat mode that is generally employed, namely, a mode that the shafthole 43 in which the rolling bearings 10 are housed is filled up withlubricant (that is commonly used as engine oil, for example).

1. A turbocharger comprising: a turbine shaft; a turbine wheel disposedon a first end portion of the turbine shaft in an exhaust passage of aninternal combustion engine; a compressor wheel disposed on a second endportion of the turbine shaft in an admission passage of the internalcombustion engine; a rolling bearing rotatably supporting the turbineshaft within a shaft hole of a housing; and a sealing structureperforming a sealing between the shaft hole and the exhaust passage,wherein the sealing structure includes a labyrinth seal provided betweenan outer periphery of the first end portion of the turbine shaft and thehousing, and a piston ring seal disposed on a side toward a center ofthe turbine shaft in an axial direction thereof from a position on theturbine shaft at which the labyrinth seal is provided, and wherein aring groove is formed along a circumferential direction of the housingin a middle portion of the labyrinth seal to reverse a flow direction ofexhaust gas entering from the exhaust passage.
 2. A turbochargeraccording to claim 1, wherein a coolant water jacket in which coolantwater for cooling the turbine shaft is circulated is provided on aradial outer side of the turbine shaft from the position of the housingat which the labyrinth seal is provided.